1. Field of the Invention
This invention relates to a bright heat-treating furnace, and more particularly to fluidized-bed type carburizing furnace means to be used as a bright heat-treating furnace.
2. Description of the Prior Art
As a furnace for bright heat treatment, the carburizing furnace means composed of a pair of fluidized-bed type furnaces, one for bright hardening and the other for bright tempering, which is disclosed as in Japanese Patent Publication No. SHO 60(1985)-43,409 (applicant for patent: KABUSHIKI KAISHA KOMATSU SEISAKUSHO.) has been available for actual use.
In the conventional carburizing furnace means, the furnace gas (such as, for example, N.sub.2 gas or some other atmospheric gas) used for fluidization in the bright hardening furnace is introduced through piping means into the bright tempering furnace, wherein the heat released from the furnace gas is utilized for the purpose of tempering. The furnace gas which has been introduced into the bright tempering furnace and consequently deprived of heat is passed through piping means and returned to the bright hardening furnace by means of a blower or fan disposed in the piping means.
By circulating the furnace gas in the manner described above, recycling of the heat and the composition of the furnace gas and stabilization of the conditions of the furnace gas in the two furnaces are attained.
In the conventional carburizing furnace means described above, since the fan which is used for the circulation of the furnace gas has no heat-resisting property, the furnace gas departing from the heating furnace must be cooled to a prescribed temperature. This furnace means, therefore, inevitably entails the poor economy that both the furnaces are required to be kept in operation even when no use is found for the treatment of tempering.
The conventional bright heat-treating furnace of another class using only a heating furnace has the disadvantage that, for the purpose of lowering the temperature of the furnace gas, the furnace is inevitably required to be provided with a large heat exchanger.
Further, where a mixture of nitrogen gas with an alcohol is used as the gas for fluidization, there is the possibility that soot deposits on the internal wall surface of the pipe laid between the outlet of the heat exchanger and the fluidized-bed gas dispersion plate in the carburizing furnace. If the alcohol content of this mixture is decreased for the purpose of preventing this deposition of soot, there ensues the disadvantage that desired stabilization of the internal gas of the furnace is no longer obtained. Solution of this problem necessitates additional incorporation in the furnace of a gasifier for the alcohol. Moreover, the fan used in this furnace is required to be made of a material highly resistant to heat.